High quality, quantitative microscopy and image analysis is essenfial for each of the projects in this program. The research goals in each lab are also expanding into new and more challenging imaging applicafions such as live fime-lapse microscopy and quantitative morphometry. Each of the program labs has accumulated different tools and some expertise over time, however, it will be essential to create a formal process to give access to these tools, exchange this expertise and provide computational tools for image analysis. In this way, and maintain a continuous flow of information. As part of a recent reconflguration of the microscopy resources for the Artavanis-Tsakonas and Van Vactor groups, the major microscopes owned by these two labs can now be located in a common space under supervision of Dr. David Van Vactor. Dr. Van Vactor also serves as the Chair of the Microscopy Committee of the Cell Biology Department, providing faculty oversight for many other shared instruments housed in the Nikon Imaging Center at Harvard Medical School (NIC(gHMS), a state-of-the-art facility that will be made accessible to all participants in this program project. With the recent shift to digital microscopy required to support dynamic and quantitative imaging projects and the need for a range of confocal imaging techniques. Dr. Van Vactor and the Cell Biology Department created a core facility for state-of-the-art imaging. The result was an unprecedented partnership between Harvard Medical School (HMS) and Nikon Instruments, Inc. This facility (NIC(gHMS) now houses five instruments specialized for different types of confocal applications: two laser-scanning confocals, two spinningdisc confocals (one with environmental control chamber), and a total internal reflection fiuorescence (TIRF) microscope (using evanescent wave illumination from a laser source). Dr, Van Vactor designed the facility, negofiated with the supporting vendors (eight in all), and provides confinued faculty oversight. The NIC@HMS is located in the LHRRB building near his lab allowing him to provide frequent supervision and interacfion with the facility Director, Dr. Jennifer Waters. The NIC@HMS resource is very valuable, particularly for confocal applicafions, however, there is a major drawback: the user group includes all HMS Departments. This limits the use of the facility to a weekly maximum for each group (8 hours or less). While such limits are not and issue for limited confocal projects, they are very problematic for the routine image acquisition and processing required by the program project labs for analysis of screen data. Therefore, it is vital for the program project to maintain its own, complementary resources for microscopy and image processing. Since both our own core in Dr. Van Vactor's lab and the NIC(gHMS are in the same building, it is easy for our research staff to move quickly from one to the other. As is evident from the description of each project all four research teams have a need for high quality, quantitative microcopy and image analysis. We are thus expecfing that all four groups will be using this core.